Master Naturalists: Barn owls' ways help us

By Paul and Mary Meredith
May 9, 2013 at 12:09 a.m.

A mature barn owl roosts during the day in a large palm right by the front doors to the Welder Wildlife Foundation near Sinton. Barn owls will roost and nest in barns because their preferred nocturnal prey, mice, live there, too.

Barn owls are found almost all over the U.S., and their numbers are largest in California and the Southwest. That's good for us around here.

But their numbers are naturally limited by availability of prey and suitable nesting sites. They cannot be purchased, placed wherever they are wanted or needed and be expected to stay in that area.

How barn owls help

The agriculture industry finds barn owls attractive assets because the owls can control rodents better than traps, poison, etc. and at no cost. When nearing maturity, barn owls eat the equivalent of 12 mice a night if mice are available. Adult barn owls nightly eat the equivalent of one large rat, gopher or small rabbit. For their weight, that's twice as much as any other owl consumes.

Some helpful body characteristics for catching prey

To get all they need to eat, barn owls use several characteristics of their bodies. Like us, their eyes face forward. But birds cannot rotate their eyes, so they compensate by using a motion we've all seen them do. They bob their heads up and down and move them from side to side.

Those movements improve their stereoscopic views and ability to judge distances. But, for night hunters, they don't have large eyes. But tests of their hearing have shown that they have the most acute hearing of all animals tested. They likely locate prey using their hearing.

How their hearing works

Feathers in the ruffs on their faces provide one part of their hearing ability. Their movable ear flaps provide another part. They move their ear flaps to form ruff feathers into cones that funnel and amplify sounds into troughs that lead to their ear canals.

One of our older relatives used what may be a similar device - a curved ear horn to capture sounds and route them to her ear hole to improve her poor hearing capacity.

Moreover, their ear flaps and ear canals are located asymmetrically on their heads. Barn owls have one ear canal pointing more toward the ground and the other one pointing more straight out from the side of their heads.

This greatly improves their hearing and capacity for locating prey. They can detect sound made by prey in the dark in two different directions and locate their prey more accurately, making them silent killers of nocturnal rodents.

In addition to the rest of their hearing system, each ear of barn owls is tuned to detect slightly different frequencies of sound. Other owls have varying sources of asymmetry that improve their hearing abilities, also based on body characteristics. For example, one species has what has been called a misshapen skull.

These physical characteristics are some - not all - of what barn owls have.

Where barn owls live, hunt

Barn owls are fairly cosmopolitan and associate with man more closely than other owls. They hunt in areas cleared for agriculture, particularly meadows and pastures.

Moreover, one place they will roost is in buildings. They also roost in some man-made nests constructed in trees, among other things. Some locations and types of nests can cause the owls problems.

Sources:

David Allen Sibley, "The Sibley Guide to Bird Life and Behavior," National Audubon Society

David Allen Sibley, "The Sibley Guide to Birds," National Audubon Society

Fred J. Alsop III, "Birds of Texas," Smithsonian Handbook

Paul and Mary Meredith are master naturalists. Contact them at paulmary0211@sbcglobal.net.